From the author of

From the author of

Dancing sometimes intimidates animators, but it actually can be quite fun.
If the music is good, you get to listen to it all day, plus you get to dance
in front of your computer and call it work. (Of course, if the music is lousy,
you still have to listen to it all day.)

When you're animating dance moves, the key is make sure that everything
happens to the beat. If your timing matches that of the music, then it should
all sync up, regardless of where it is in relation to the music.

Understanding Tempo

The key to animating dance is to let the tempo of the music drive the
animation. Determining the tempo simply requires a watch. Count the number of
beats in six seconds of music. Multiply this by 10 to get the beats per minute
(BPM). When you have this, you can determine how many frames you'll need
per beat of music. For example, a common BPM is 120. At 24 frames per second
(fps), the frames per beat would be this:

24 fps x 60 seconds = 1440 frames/minute (fpm)

1440 fpm/120 BPM = 12 frames/beat

Here's a quick table for a range of tempos.

BPM

24 fps

30 fps

100

14.4 frames/beat

18 frames/beat

110

13

16.4

120

12

15

130

11

13.8

140

10.3

12.8

This table shows how, at some tempos, the frames per beat is a
fractional number. This is one of the problems of a fixed frame rate. The best
thing to do in this case is to round up or down to the nearest number and
animate at that rate. Unless the shot is extremely long, the characters should
sync up within a frame or two, which the audience will not notice.

Of course, if you want to be precise, or if the shot is particularly long,
you can certainly read the track and mark down exactly which frames the beat
hits. In this case, you will never be more than a half frame off on your sync.

It must be noted that characters can dance with or without music. If the
character is dancing an unaccompanied jig of joy, then you can just pick a tempo
and go with that. I usually pick 120 BPM, simply because it's easy at a
half second per beat.

The classic animation studios used to record their music to a fixed
metronome. By knowing the beat of the music, the animators could animate even
without the soundtrack. Warner Brother cartoons were usually animated at 120
BPM, with most major moves occurring in multiples of 6 or 12 frames.